Subclassing Dictionaries

The process differs by Python version.

Python-2.2

Derive from dict.

ex:

 1 class Msg(dict):
 2 
 3  __slots__ = [] # no attributes
 4 
 5  def __init__(self, msg_type, kv_dict = {}):
 6  dict.__init__(self)
 7  self["msg-type"] = msg_type
 8  self.update(kv_dict)
 9 
 10  def Type(self):
 11  return self["msg-type"]
 12 
 13  def __getitem__(self, k):
 14  return self.get(k, None)
 15 
 16  def __delitem__(self, k):
 17  if self.has_key(k):
 18  dict.__delitem__(self, k)
 19 
 20  def __str__(self):
 21  pp = pprint.pformat(dict(self))
 22  return "%s: %s" % (self.Type(), pp)

The __slots__ line indicates that Msg has no attributes of its own, preserving memory; see UsingSlots.

See Also

Python-2.2, SubclassingBuiltInTypes, UsingSlots

Questions

• Is this bad Python-2.2 code? Make improvements..! I do think it's worth showing how to use slots in the context of subclassing dict; In many cases, I think, people would want to do it. I do wonder if slots should be specified before or after the initializer- something to put on the UsingSlots page. -- LionKimbro 2003年09月07日 17:07:24 lwickjr: Before, I think, collected with the other declaritives.